The present invention relates to a method and an apparatus for determining quality of a gearing system having at least two gear wheels, and in particular a method and an apparatus which, by using angle of rotation differences between a plurality of measured output angles of rotation and theoretical output angles of rotation of a second gear wheel, can obtain a quality measure of the gearing system.
Many precision instruments include gearing mechanisms, and in particular toothed wheels which form these gearing mechanisms. The mechanisms often implement rotation or other movement of a part of the instrument, e.g. a head part or arm. For example, simple microscopes contain gearing mechanisms realized by toothed wheels which enable minimal changes in the distance between the objective and the object table by rotating an adjustment wheel. To generate a consistent movement it is important for the toothed wheels to be shifted with minimal play, their individual teeth being engaged with one another. Optimal operation is best achieved by there being an optimal distance between the toothed wheels, and by the toothed wheels being uniform.
In measuring technology, e.g. surveying technology, gearing mechanisms in measuring instruments, in particular surveying instruments, such as e.g. tachymeters, theodolites or total stations also play a large role. Such instruments are used for measuring distances and/or angles of objects. These measuring instruments usually have a base unit with a stand for the stable positioning of the measuring instrument on the ground, and a head unit which can be moved in relation to the base unit. The head generally includes an optical device, such as a distance measuring device or a targeting apparatus for targeting or focusing on an object, for example, a lens, a telescope, a camera or similar item. In particular, to be positioned so that it can target an object, the head unit must be rotatable within the space, preferably in a vertical and a horizontal direction, which can be achieved by an appropriate gearing mechanism.
The moveable or rotatable head unit can provide a distance measuring device or a targeting apparatus for targeting a distant object to determine the location of the distant object. Different types of gearing mechanism or drives are known for rotating the head unit relative to the base unit in a horizontal plane. It is possible, for example, to provide the distance measuring device of the head on a gimbal-mount bracket so as to also be moveable in a vertical direction.
In surveying instruments, such as e.g. geodetic measuring instruments, the rotation of the head unit can be brought about by using a motor, for example, a direct current drive motor, so that the head unit can be accurately moved relative to the base unit. When setting a specific angle it is important here to provide a high degree of accuracy, preferably being below 1″. Such accuracy leads to quality requirements being made of the gearing mechanism which rotates the head unit.
The double flank gear test is a known test for toothed wheels of a gearing mechanism. The double flank gear test is used for simply testing gear teeth, i.e. the points or spikes of toothed wheels or similar geared wheels. The principle of the double flank gear test is based upon a master toothed wheel, which is highly precise, and a toothed test wheel, which represents the workpiece, being shifted toward one another without play. A corresponding test apparatus is designed such that one axis of rotation is fixed and the other axis of rotation of the other toothed wheel is variable. With efficient dimensional and form stability of the toothed wheels, the axis distance remains constant during shifting. Deviations from the ideal form of a toothed wheel lead to fluctuations in the axis difference between the two toothed wheels.
Although the double flank gear test is an established test method, it can only be applied to gearing mechanisms under certain conditions. The examination of the gearing mechanism of a measuring instrument or some other precision instrument, such as a microscope, would require the testing of the individual toothed wheels of the gearing mechanism in a double flank gear test. The quality of the individual toothed wheels thus could be tested, but the interplay of the toothed wheels of the gearing mechanism, in particular the distance between the latter, cannot be examined. In addition, automatic matching of the distance between the toothed wheels of a gearing mechanism is also not possible either.
Consequently, there is a need to provide a method and an apparatus for determining quality of a gearing system having at least two gear wheels which enables matching of the toothed wheels of the gearing system and determination of the quality of the gearing system.